What brand sensors?

 

If your plugs looked good, I would not suspect a bad O2 sensor. Wouldn't the plugs be black if engine was running rich? If you want to continue troubleshooting O2 sensors, you can unhook them and see if you get 5v on the live data feed.
I wouldn't suspect blown head gasket since plugs were not fouled by coolant.
You mentioned mushy pedal. Does it feel soft even with engine off? I doubt it is affecting your gas mileage but may lead you to the problem.
Does your truck idle smooth and sound good at high rpm?
How many miles on your truck? How long have your had it? Any major maintenance or events, like a wreck or overheat?
Some inexpensive maintenance you can do is clean the injectors, and, check continuity of spark plug wires. I assume you have the long wires that reach across the engine.

 

Had the truck since 2016. 185000 miles. Never overheated. This is a list of all the things I have done to it-

-Oil change every 5000 miles with Mobil 1
-Rear fenders and rockers replaced
-Water pump, both rad hoses, idler pulleys
-exhaust manifold bolts
-entire new exhaust system & cats
-power steering pump and power steering rack
-new outer tie rods
-new front wheel bearings
-new fuel pump twice
-new wiper motor
-new battery
-new u joints
-new tires
-new throttle body
-new MAP
-spark plugs
-new brakes

Yes it has the long wires.

 

You might try pulling the airbox off and run the engine in the dark. Check for spark scatter and arching.
Any brakes dragging / heating up? Parking brake intact? My right rear lining actually came off the shoe and was floating around. I found that out when I did my brakes.

You are already way beyond this. When I lost mileage on my '05 5.7 Ram, per the trip computer, I went from 18 (65 mph on flat road no wind) down to 13 mpg over a couple years. New plugs, air filter, Seafoamed half of my 32 gallon tank, and it didn't help a bit.
Pulled of the air box, looked down the throttle body, and found it was caked with crankcase blow-by buildup. Spent about 45 minutes with several Seafoam soaked rags wiping the grime out as far as I could reach. I got my mileage back.

 

I did use the spray Seafoam in the air box. I will try some more. Could yours have been from a dirty IAT sensor or just dirty intake?
Brakes are good.

 

Another weird thing happened today. I started the truck and shut it off. I attempted to restart it and it would just crank over and sputter but not start. I primed the fuel pump by turning the key and I heard the pump run. Eventually the truck started and ran fine. Then i stopped at a light and it acted like it wanted to die, then ran fine since.

It has had issues with stalling the last few years. It is always random either driving or stopped.

Mpg went up since new fuel pump from 7-8 to 9.

 

I can't say for sure. Other than disconnecting and reconnecting the IAT plug, I didn't touch it. A faulty connection? Perhaps.
Leaving TB on the truck, I just wiped it clean as far down I could reach in the TB with the plate open. Even the plate was caked up. Leaning toward the grime in my case.

 

I've been doing some researching. I noticed that sometimes when it is gutless it is when there is heavy load on the engine but it wont shift down to 1st gear from 2nd. My research online is pointing to the governor pressure sensor. I am going to try that.

 

Did you ever figure out the issue?